Habitable planets around the star Gl 581?

Radial velocity surveys are now able to detect terrestrial planets at habitable distance from M-type stars. Recently, two planets with minimum masses below 10 Earth masses were reported in a triple system around the M-type star Gliese 581. Using results from atmospheric models and constraints from the evolution of Venus and Mars, we assess the habitability of planets Gl 581c and Gl 581d and we discuss the uncertainties affecting the habitable zone (HZ) boundaries determination. We provide simplified formulae to estimate the HZ limits that may be used to evaluate the astrobiological potential of terrestrial exoplanets that will hopefully be discovered in the near future. Planets Gl 581c and 'd' are near, but outside, what can be considered as the conservative HZ. Planet 'c' receives 30% more energy from its star than Venus from the Sun, with an increased radiative forcing caused by the spectral energy distribution of Gl 581. Its habitability cannot however be positively ruled out by theoretical models due to uncertainties affecting cloud properties. Irradiation conditions of planet 'd' are comparable with those of early Mars. Thanks to the warming effect of CO2-ice clouds planet 'd' might be a better candidate for the first exoplanet known to be potentially habitable. A mixture of various greenhouse gases could also maintain habitable conditions on this planet.Comment: Astronomy and Astrophysics (2007) accepted for publicatio

Collective motion of self-propelled particles interacting without cohesion

We present a comprehensive study of Vicsek-style self-propelled particle models in two and three space dimensions. The onset of collective motion in such stochastic models with only local alignment interactions is studied in detail and shown to be discontinuous (first-order like). The properties of the ordered, collectively moving phase are investigated. In a large domain of parameter space including the transition region, well-defined high-density and high-order propagating solitary structures are shown to dominate the dynamics. Far enough from the transition region, on the other hand, these objects are not present. A statistically-homogeneous ordered phase is then observed, which is characterized by anomalously-strong density fluctuations, superdiffusion, and strong intermittency.Comment: Submitted to Physical Review

The impact of in-season national team soccer play on injury and player availability in a professional club

This study investigated the impact of in-season national team duty on injury rates and player availability in a professional soccer club. Time-loss injuries and exposure time during club and national team duties were recorded prospectively over 5 seasons (2009–2014). A time-loss injury was sustained by 37.7% of squad members participating in national duty, all injuries occurring in match-play. The incidence (per 1000 h exposure) for national team player match-play injuries did not differ (P = 0.608) to that for all players in club competitions: 48.0 (95% CI 20.9–75.5) vs. 41.9 (95% CI 36.5–47.4), incidence rate ratio = 1.2 (CI: 0.8–2.4). The majority (58%) of national team injuries resulted in a layoff ≤1 week. Of all working days lost to injury generally, 5.2% were lost through injury on national duty. Injury incidence in the week following national duty was comparable (P = 0.818) in players participating or not: 7.8 (95% CI 3.6–12.0) vs. 7.1 (95% CI: 4.6–9.6), incidence rate ratio = 1.1 (CI: 0.7–2.7). While approximately 40% of participating players incurred a time-loss injury on national duty, no training injuries were sustained and injuries made up a negligible part of overall club working days lost to injury. Following duty, players had a similar injury risk to peers without national obligations

A minimal model for spontaneous cell polarization and edge activity in oscillating, rotating and migrating cells

How the cells break symmetry and organize their edge activity to move directionally is a fun- damental question in cell biology. Physical models of cell motility commonly rely on gradients of regulatory factors and/or feedback from the motion itself to describe polarization of edge activity. Theses approaches, however, fail to explain cell behavior prior to the onset of polarization. Our analysis using the model system of polarizing and moving fish epidermal keratocytes suggests a novel and simple principle of self-organization of cell activity in which local cell-edge dynamics depends on the distance from the cell center, but not on the orientation with respect to the front-back axis. We validate this principle with a stochastic model that faithfully reproduces a range of cell-migration behaviors. Our findings indicate that spontaneous polarization, persistent motion, and cell shape are emergent properties of the local cell-edge dynamics controlled by the distance from the cell center.Comment: 8 pages, 5 figure

Superconducting instability in the Holstein-Hubbard model: A numerical renormalization group study

We have studied the d-wave pairing-instability in the two-dimensional Holstein-Hubbard model at the level of a full fluctuation exchange approximation which treats both Coulomb and electron-phonon (EP) interaction diagrammatically on an equal footing. A generalized numerical renormalization group technique has been developed to solve the resulting self-consistent field equations. The $d$-wave superconducting phase diagram shows an optimal T_c at electron concentration ~ 0.9 for the purely electronic Hubbard system. The EP interaction suppresses the d-wave T_c which drops to zero when the phonon-mediated on-site attraction $U_p$ becomes comparable to the on-site Coulomb repulsion $U$. The isotope exponent $\alpha$ is negative in this model and small compared to the classical BCS value $\alpha_{BCS} = 1/2$ or compared to typical observed values in non-optimally doped cuprate superconductors.Comment: 4 pages RevTeX + 3 PS figures include

Implications of the isotope effects on the magnetization, magnetic torque and susceptibility

We analyze the magnetization, magnetic torque and susceptibility data of La2-xSrxCu(16,18)O4 and YBa2(63,65)CuO7-x near Tc in terms of the universal 3D-XY scaling relations. It is shown that the isotope effect on Tc mirrors that on the anisotropy. Invoking the generic behavior of the anisotropy the doping dependence of the isotope effects on the critical properties, including Tc, correlation lengths and magnetic penetration depths are traced back to a change of the mobile carrier concentration.Comment: 5 pages, 3 figure

The Isotope Effect in d-Wave Superconductors

Based on recently proposed anti-ferromagnetic spin fluctuation exchange models for $d_{x^2-y^2}$-superconductors, we show that coupling to harmonic phonons {\it{cannot}} account for the observed isotope effect in the cuprate high-$T_c$ materials, whereas coupling to strongly anharmonic multiple-well lattice tunneling modes {\it{can}}. Our results thus point towards a strongly enhanced {\it{effective}} electron-phonon coupling and a possible break-down of Migdal-Eliashberg theory in the cuprates.Comment: 12 pages + 2 figures, Postscript files, all uuencoded Phys. Rev. Lett. (1995, to be published

Les salicornietum emerici et ramosissimae du littoral méditerranéen français

En este trabajo, los áutores señalan precisiones taxonómicas y corológicas sobre las Salicornias anuales del litoral mediterráneo francés. Salicornia emerie!, tetraploide y Salicornia ramosissima diploide tienen una distribución mediterránea, atlántica alcanzando Bretaña y el 5. de Inglaterra. En el Mediterráneo definen dos asociaciones territoriales, Arthocnemo-Salieornietum emerieiy Arthorocnemo-Salicornietum ramosissimae la primera en la franja interna y la segunda en la franja externa de las lagunas sobre sustrato mineral clorurado y sujeto a desecación estival